1. Field of the Invention
The present invention relates to a scroll compressor, and more particularly, to a variable capacity scroll compressor, which is configured to vary an exhaust volume of the compressor in multi-stages.
2. Description of the Related Art
Generally, a cooling system is applied to an air conditioner or a refrigerator to lower the temperature of an enclosed space by absorbing and discharging heat using refrigerant circulating a cooling cycle.
Such a cooling system is configured to perform a series of cycles of compression, condensation, expansion and vaporization of refrigerant. A scroll compressor is used to perform the compression cycle among the series of cycles.
Since the scroll compressor is disclosed in a plurality of published documents, the detailed description on the general structure and operation will be omitted herein.
The reason why the compression capacity of a scroll compressor should be varied will be described hereinafter.
A scroll compressor for a specific use is generally selected by considering the most disadvantageous operation condition when forecasting its use environment, for instance, the greatest compression capacity-requested condition (i.e., a heating operation of an air conditioner using heat pump).
However, it is general that the most disadvantageous condition does not nearly occur in an actual operation. In an actual operation of the compressor, a condition needing a small compression volume (ex. cooling operation of air conditioner) not the most disadvantageous condition exists too.
Thus, when the compressor having a large compression capacity is selected considering the worst condition, the compressor is operated under the low-load condition during an operation period of the high-compression ratio, thereby deteriorating an overall operation efficiency of the system.
Therefore, in order to improve the overall operating efficiency even under a normal operating condition and to accept the operational condition under the most disadvantageous condition, there is a need for a compressor that has a variable compression capacity.
To vary the compression capacity of the scroll compressor, a method for electrically controlling an RPM of the compressor has been most widely used.
Such an electrical control method has an advantage of effectively varying the compression capacity. However, additional components, for instance, an inverter for accurately controlling the RPM of a motor, are required. Furthermore, when the motor rotates with a relatively high RPM, it is difficult to ensure a reliability of frictional portions.